1. Field of the Invention
This invention relates to electrical instruments for associating elements of an electrical circuit of a building's electrical system and distinguishing different circuits from one another.
2. Discussion of the Prior Art
In electrical work, it is oftentimes necessary to associate different parts of an electrical circuit in a building with one another, or to distinguish one circuit from another. For example, before doing electrical work in one area of a building that has several electrical circuits, one should turn off the electrical circuit interrupter, e.g., a fuse or circuit breaker, that is associated with the particular electrical circuit which serves that area. The different areas of the building are typically wired into an electrical power distribution panel. Such power distribution panels, usually filled with fuses or circuit breakers, are often found near the electrical power service entrance inside a building such as a home, office, apartment, or factory. The interrupter that controls the outlets, light fixtures or other electrical equipment for the desired area must be identified and turned off. As another example, one may want to determine which outlets, switches or other electrical equipment are on the same electrical circuit.
Traditional methods of associating different circuit elements in a building with one another can consume much time through the process of trial and error, can require the services of 2 or more persons, and can produce needless power outages through the inadvertent switching of unrelated circuit interrupters.
There are a number of prior devices for identifying individual circuits in the electrical wiring system of a building. Patents such as U.S. Pat. Nos. 3,076,931, 3,623,142, and 3,924,179, disclose locators that require that the circuits be de-energized or in some way disconnected from the main electrical supply. U.S. Pat. No. 4,121,152 discloses a locator which uses a pulsed load connected to a live outlet, which could cause tripping of GFCI outlets or of the circuit interrupters. The pulsed load can be determined by the use of a clip-on ammeter. This requires opening the control panel and exposing the user to bare conductors therein. It also requires an expensive clip-on ammeter.
U.S. Pat. Nos. 4,906,938 and 5,497,094 disclose circuit locators that use an electrical device known as a SIDAC to generate non-coherent current pulses. There is an associated broadband receiver to receive or detect the pulses at the power panel. The device has a manually operated adjustment dial for the user to operate so as to distinguish one circuit from another. The dial is adjusted while moving the device over the interrupters until the device beeps or lights up when it is in the vicinity of only one interrupter. This device also may encounter difficulty in the presence of electrical noise generated by SCRs or Triacs, which are sometimes used in building electrical equipment, such as light dimming circuits, motor controller circuits, etc.
Other devices are commercially available that use a transmitter that generates short bursts of current derived from crystals, thereby generating a magnetic signature which can be sensed by the receiver. The crystals are relatively expensive, and these devices require a sophisticated generator and associated receiver.
It is desirable that a circuit finder be simple to operate and not require the operator to manually adjust the device. The finder should also permit performing the test without de-energizing the system, as other important electrically operated equipment such as a computer may be on the branch circuit. The device should be able to perform well in the presence of a large amount of electrical noise generated by equipment operating on the circuits and should not cause a circuit breaker or a ground fault circuit interrupter (GFCI) to trip. The device also should not require disassembly of the power panel or circuit element being probed and should be easy and inexpensive to manufacture.